Process for aftertreatment of liquids, in particular clarified juice, and unit for performing the process

ABSTRACT

For aftertreatment of clarified juices, the juice is brought into contact with an agent, e.g., PVPP, and is filtered in a crossflow filtration device (11) and the aftertreated juice is separated as permeate from the agent. The agent can be regenerated by the addition of water and lye either inside or outside the unit. After regeneration, the lye is again flushed out by diafiltration on the permeate side of crossflow filtration device (11). With the aid of crossflow filtration, the economic efficiency and the universal applicability with respect to the use of agents of the unit can be considerably increased and the treatment quality of the juice can be improved.

The invention relates to a process for aftertreatment of at leastpartially clarified liquids, in particular clarified juices of fruits,berries or vegetables, in each case with an agent to prevent subsequentclouding and/or for color lightening, and the juice is brought intocontact with the agent and the agent is retained by a filter.

In some cases, a subsequent clouding of the juice occurs afterclarifying juice, especially during clarification by ultra-ormicro-filtration, after a certain storage time and under certainconditions, for example after concentration. To prevent this, inpractice the treatment of the juice with an agent, the so-called PVPP(polyvinylpolypyrrolidone), which is able to bond selectively thepolyphenols that cause subsequent clouding, has proven itself veryreliable. PVPP is a fine powder that is added at a concentration of, forexample, 10-100 gr/HL to the juice to be aftertreated and, after aretention time of, e.g., about 5 minutes, is again filtered out of thejuice, which afterwards is clouding-stable. Since PVPP is relativelyexpensive, units are mainly used in which the PVPP can be recovered. Thesame treatment is also used if a lightening of the juice is desired.

A known process for aftertreatment of clarified juice consists in thatto the clarified juice that is delivered from an ultra-, micro- orconventional filtering unit there is added the agent PVPP and themixture of clarified juice and PVPP flows through a precoated filter.With the aid of a dosing device, the PVPP concentration in the juice isadjusted. Inside the precoated filter, the suspended PVPP is retained bythe filter surfaces, so that the exiting juice is free of PVPP. Anotherfiltration of the juice occurs by another filter which, for safetyreasons, is connected downstream from the precoated filter and ensuresthat no more PVPP is contained in the juice. As time goes by the filtercake consisting of PVPP keeps on getting thicker on the precoatedfilter. The throughput becomes correspondingly smaller until the unitmust be shut off. After shutting off the juice feed, so-called washwater and lye flow through the deposited PVPP or the filter cake. Therelatively expensive PVPP is regenerated by the lye and, by dissolvingthe filter cake and bringing it into the dosing device, it can be usedagain.

The suspended form of pulverulent agents such as, e.g., PVPP, activatedcarbon or fining agents such as bentonite, etc., in the juice, offerideal conditions for a good mass transfer between juice and agent toremove undesired matter from the juice, for example by adsorption on theagent, as well as for the operation of the process.

But the known process of precoated filtration has the drawback that thesuspended agent is deposited relatively quickly on the filter surfacesby the static filtration and a precoat layer forms. The result of thisis a lesser effectiveness of the PVPP, which is now present in the formof a so-called fixed bed that is relatively thin and is quickly flowedthrough. The matter responsible for clouding the juice is thus often notbroken down sufficiently with the concentrations for, e.g., PVPP to someextent allowed by law. Further, the growing filter layer causes acorrespondingly increasing reduction of the throughput. Another drawbackconsists in the fact that only agents can be used which, because oftheir structure, generate a relatively well permeable filter precoatingand thus guarantee an economical throughput. This is achieved with aspecial PVPP agent, but which is considerably more expensive than thenormal PVPP that is already expensive in itself. This also causesincreased operating costs, since the loss of agent during regenerationis about 1-2%. Further, it is a drawback that the process must beinterrupted independently of the throughput as soon as the filter layerhas reached a certain size, which is given by the distances between thefilter elements. The higher the concentration of the suspension, thefaster this state is reached. Further, the PVPP regeneration requiresrelatively many operations. With untrained operating personnel, anexpensive automation of the work cycle can thus become necessary. Withthe precoated filtration process, no aftertreatment with soluble agents,e.g., with enzymes, can be performed either.

In another known embodiment for aftertreatment of juice, layerscontaining PVPP are built into a so-called sheet filter. Juice flowsthrough these sheets and is treated with PVPP this way. The contact timeof the juice and the agent is short in this case. Because of this,relatively large apparatuses and a frequent regeneration of the agentare necessary. Further, only use of regenerated pretreatment agents issuitable considering the expense. Soluble aftertreatment agents are alsonot usable.

The object of the invention is to provide a process and a unit foraftertreatment of clarified juice by which, with reduced investmentcosts, the throughput and economic efficiency of the unit are increasedand the quality of the treatment is improved. This object is achievedaccording to the invention in that the mixture of juice and agent isfiltered in the crossflow filtration process.

Other advantageous and suitable embodiments of the invention are to begathered from the claims.

The advantages achieved with the invention consist especially in that bythe crossflow filtration, because of a dynamic filtration, the formationof a precoat layer on the filter surfaces that reduces the throughputand the effect of the agent is prevented. In this way, the economicefficiency of the unit is increased. The unit works with suitable filterselection practically loss-free, as long as a regeneration of the agentis possible. The activity of the agent can be balanced by varying andcontrollable retention times in the juice. With the aid of crossflowfiltration, a simple concentration of the agent-suspension or solutionis possible for regenerating the agent by which, despite the suspendedor dissolved form of the agent, the regeneration time and the necessaryamount of regeneration agent can be kept in economically feasiblelimits. Further, a universal use of various agents is possible. BesidesPVPP, other pulverulent agents such as, e.g., bentonite, activatedcarbon, etc., can be used.

The invention is explained in more detail in the following descriptionand the drawing, which represents various embodiments. There are shownin:

FIG. 1, a diagrammatic representation of the unit with regeneration ofthe agent inside the unit and

FIG. 2, the unit according to FIG. 1 with regeneration outside the unit.

As can be seen from FIG. 1, the juice to be aftertreated is introducedby a feed line 2, which can be shut by a valve 1, into an initial tank3. Initial tank 3 is made column-shaped in the vertical direction andexhibits several charging points 4 through which the juice canselectively be introduced into initial tank 3. For this purpose, therebranches off from feed line 2 a line 5 which, by shutoff valves 6, leadsto various charging points 4 of initial tank 3. An agitator 7 withseveral agitating propellers 8 and stator components 9 is placed ininitial tank 3.

From the bottom end of initial tank 3, a line 10 leads to a crossflowfiltration device 11, which can consist of an ultra-, micro- or coarsefiltration unit. A circulating pump 12 is connected in line 10. A returnline 13 leads from crossflow filtration device 11 back to initial tank3. Line 10, crossflow filtration device 11, return line 13 and initialtank 3 constitute the retentate-side circuit. By a connection line 14between return line 13 and line 10, a part of the retentate can be feddirectly back into line 10 while circumventing initial tank 3. Theamount of diverted retentate can be controlled by a regulating valve 15,which is connected by a control line 16 to a color regulator placed indischarge line 17 for the permeate or to a regulator for a processvariable 18 influenced by the treatment. Another control line 19 leadsfrom color regulator 18 to shutoff valves 6 for controlling the feed offresh juice into initial tank 3 to control the duration of thetreatment.

The fresh juice delivered from an ultra- or micro-filtration device isintroduced by feed line 2 into initial tank 3 and, with the aid ofcirculating pump 12, is conveyed through crossflow filtration device 11.In this way, the juice is brought into contact with the agent, forexample PVPP, of which a dosed amount is added in advance to theretentate-side circuit. The polyphenols present in the juice that causesubsequent clouding are bonded by the PVPP, so that the juiceaftertreated this way, which is separated from the agent on the filtersurface of the crossflow filtration device, leaves crossflow filtrationdevice 11 on the permeate side through discharge line 17clouding-stable. Because of the crossflow filter principle, the agentremains in the retentate-side circuit in suspension or in solution withsoluble agents. The column-shaped structure of initial tank 3 causes newjuice, after its entrance into the initial tank only after a certainretention time during which the agent can act, to reach the filtrationsurface of crossflow filter device 11. By agitator propellers 8 andstator components 9 or, e.g., by the installation of static mixingelements, a good intermixing of juice and agent as well as a narrowretention time spectrum for the juice flowing through is achieved. Thisimproves the quality of the treatment and further reduces the necessaryconcentration of agent with respect to offering the possibility of usinga smaller tank.

The intensity of the treatment of the juice with PVPP can be regulatedby changing the retention time of the juice in the unit or byinfluencing the turbulence in initial tank 3 caused by the agitatorspeed and the circulating amount. For a shorter retention time, forexample to introduce fresh juice into initial tank 3, a charging point 4lying further below is selected by opening associated shutoff valve 6.An automatic control of shutoff valve 6 occurs by regulator 18. Anotherpossibility of influencing the retention time is made possible byregulating valve 15, which is also connected to color regulator 18 andcontrols the return flow amount of the retentate to initial tank 3depending on the color value of the juice exiting on the permeate side.The regulation of the retention time can also be performed depending onthe time of the prefiltered juice amount or on another, characterizingprocess variable.

To be able to use again the relatively expensive agent after adsorptionof the undesired matter from the juice, it must be subjected to aregeneration treatment with lye. For this, the juice feed to initialtank 3 is shut off and, by introducing water into the retentate-sidecircuit, the remaining juice is flushed out and the mixture of water andagent is concentrated. This results in a reduction of the volume to beregenerated and thus also a reduction in the amount of regenerationagent necessary. Further, the regeneration time is also shortened andthus the economic efficiency is increased. After introducing lye intothe remaining volume of the retentate-side circuit, regeneration of theagent is performed by preferably recirculating the contents of initialtank 3 through crossflow filtration unit 11 by circulating pump 12. Herethe liquid level in initial tank 3 has level N. After completion of theregeneration step the lye feed is shut off and the unit is washedthoroughly by the introduction of backwash water by feed line 20 intothe retentate-side circuit and cleaned of lye. After this, fresh juicecan again be introduced by feed line 2 and the treatment of the juicewith the regenerated PVPP can be continued.

FIG. 2 represents an embodiment in which the regeneration of the agentoccurs outside the unit. This type of regeneration is suitable if, forexample, relatively high chemical concentrations are necessary for theregeneration and/or an influencing of the treatment intensity also bychanging the agent concentration is necessary. The same applies for thecase of higher temperatures that are harmful for certain types ofmembranes of crossflow filtration unit 11, for example consisting ofplastic. To avoid these drawbacks, preferably the solution of water andagent concentrated in advance in the retentate-side circuit is pumpedfrom circulating pump 12 through a line 21 from the retentate-sidecircuit into a regeneration tank 22 outside the unit. For chemicaltreatment and regeneration of the PVPP, lye is fed to regeneration tank22 and thoroughly mixed with the aid of an agitator 23. After a certainretention time, the regeneration of the agent is finished, so that thelye contained in the mixture can again be removed. For this purpose,after cooling and dilution by backwash water, the mixture is pumped fromregeneration tank 22 preferably with the aid of a circulating pump 24through a line 25 into crossflow filtration device 11 and is washed bydiafiltration or a similar process, so that the lye can exit throughdischarge line 17 on the permeate side of crossflow filtration device11. The remaining mixture consisting of backwash water and agent isagain fed back by return line 13 of the retentate-side circuit intoinitial tank 3 or by another line 26 branched from return line 13 intoregeneration tank 22. From regeneration tank 22, the regenerated andwashed agent is introduced by a line 27 into initial tank 3 and thusinto the retentate-side circuit. Simultaneously, the juice feed can beinitiated by feed line 2, so that a new process for aftertreatment ofthe juice can occur.

The regulation of the treatment duration of the juice already describedin the embodiment according to FIG. 1 can be supplemented in theembodiment according to FIG. 2 in that simultaneously with the feed offresh juice, a gradual or regulated addition of regenerated agent occursfrom regeneration tank 22 by line 27 into initial tank 3. In line 27 aregulating valve 28 is placed, which can be controlled by a line 29 fromregulator 18.

With the use of inexpensive agents or with use in very lowconcentrations, a regeneration of the agent can optionally be dispensedwith. With agents that cannot be regenerated the regeneration iseliminated anyway.

The process and the unit according to the invention are suitable notonly for stabilizing clear juices of fruits, berries and vegetables, butcan also be used for other liquids to be aftertreated such as wine, beerand the like, as well as for lightening liquids.

I claim:
 1. Process for aftertreatment of at least partially clarifiedliquids, in particular clarified juices of fruits, berries or vegetablesto prevent subsequent clouding and/or for color lightening the stepscomprising bringing a partially clarified/juice into contact with aclarifying agent to form a mixture of juice and clarifying agent, andsubjecting the mixture of juice and clarifying agent to a crossflowfiltration process such that the clarifying agent is retained on oneside of a filter and the juice is separated through another side of thefilter from the retained clarifying agent.
 2. Process according to claim1, wherein the crossflow filtration is performed by coarse filtration,microfiltration or ultrafiltration.
 3. Process according to claim 1 or2, wherein the juice is kept in contact with the agent for apredetermined retention time.
 4. Process according to claim 3, whereinthe retention time is varied whereby the treatment intensity is changed.5. Process according to claim 4, wherein the time and/or amount of juicetreated is varied whereby the treatment intensity is controlled. 6.Process according to claim 4 or 5, wherein the treatment intensityresulting from treatment duration and/or agent concentration and/orturbulence in an initial tank is controlled in response to the colorvalue or another predetermined treatment-influenced process variable ofthe juice exiting on the permeate side after crossflow filtration. 7.Process according to claim 2 wherein the intensity can be changed by agradual and/or controllable clarifying agent is gradually andselectively added to the retentate-side circuit to change the treatmentintensity.
 8. Process according to claim 2 and the steps of cutting offthe juice feed, adding water to the retentate-side circuit such thatthis circuit is thoroughly washed, concentrating the mixture of juiceand clarifying agent in the diafiltration or a similar process andfeeding a regeneration agent to the retentate-side circuit to regeneratethe clarifying agent.
 9. Process according to claim 8, wherein afterregeneration of the agent, the retentate-side circuit is washed out bythe addition of backwash water in the diafiltration or a similarprocess.
 10. Process according to claim 9, wherein at least theregeneration of the clarifying agent is performed outside, and theflushing and washing are performed inside or outside the retentate-sidecircuit.
 11. Process according to claim 1 wherein the clarifying agentcomprises a pulverulent agent which bonds with polyphenols in thepartially clarified juice.
 12. Process according to claim 11 whereinsaid agent comprises polyvinylpolypyrrolidone.